Thanks for the responses, sounds like there are some supporters of the vented nipples. It is interesting (at least to me) that several people mentioned that removing the spent cap was easier.
The important points to me is that there seems to be qualitative evidence that the nipples provide a hotter spark and that side venting may not be a concern.
Since I have a new half dozen 1/4 x 28 nipples in my shooting box I doubt if I will use one in the near future.